Medical drama series “Brain” involves around three doctors at prestigious Chunha University Hospital.

Lee Kang-Hoon (Shin Ha-Kyun) is an excellent, but arrogant, brain surgeon at Chunha University Hospital. He came from a poor family background and is still haunted by the painful memory of his father’s death which was caused by the rejection of a doctor. Kang-Hoon has a strong desire to succeed and prove that he is the best. His rival is Joon-Suk (Jo Dong-Hyeok) who comes from a family of doctors and has basically everything. Kim Sang-Chul (Jung Jin-Young) is known as the best brain surgeon at Chunha University Hospital. He also cares about his patients and has a strong dislike for Kang-Hoon.

One day, a young man collapses at an indoor swimming pool and is sent to the hospital. The patient is Unconscious on arrival. Kang-Hoon gives the order to prepare for surgery, but Joon-Suk suggests that they call Kim Sang-Chul to perform the surgery. Kang-Hoon replies that there isn’t enough time and performs the surgery himself, while other doctors observe the operation.

During the surgery, there’s a dangerous moment when the patient’s aneurysm ruptures. At this time, Joon-Suk calls Kim Sang-Chul. Kim Sang-Chul runs to the operation room. Meanwhile, Kang-Hoon manages the operation well and the surgery is a success, but he leaves the last clip for the vice director of the hospital. Kang-Hoon wants to gain the favor of the vice director. Because of her arrogant attitude, he isn’t welcome by anybody at the hospital.

While, Kang-Hoon takes a rest in his office he receives a phone call from his younger sister. Kang-Hoon says he is busy and hangs up. He attends a conference of junior doctors. There Kang-Hoon asks questions to the junior doctors, but none of them are able to answer his questions. Kang-Hoon then asks for their chief doctor who is Ji-Hye (Choi Jung-Won). Ji-Hye is not there. Kang-Hoon yells at them to follow him.

On the way, Kang-Hoon and his partiy happens to meet Kim Sang-Chul and Ji-Hye. Kim Sang-Chul blames Kang-Hoon for not checking on his patient after the surgery.

When Kang-Hoon is back in his office, he begins to blame the others and especially Ji-Hye, who did not graduate from Chunha University. Ji-Hye talks back to Kang-Hoon. Kang-Hoon decides to seek revenge by giving out work. While Ji-Hye is writing a report asked for by Kang-Hoon, Joon-Sook surprises her. Ji-Hye replies that she can’t understand why Kang-Hoon has such a strong dislike for her. Joon-Suk tells her not to confront Kang-Hoon. At the cafeteria, Kang-Hoon eats lunch alone. Joon-Suk asks Kang-Hoon to be nice to Ji-Hye. Kang-Hoon aks him whether he likes her.